A Modern Frigate Design

Sorry for taking so long to get back to this. I had a couple health related issues to deal with this week.

Looking at the data that I have posted for the FFG-7 and using what I believe was its initial design weapons and sensor fit (plus the listed weight allowances given for the CIWS, TACTASS, ECM and such) I have come up with an initial weight estimate of 137.9 mt for Group 400 (Sensors) and 90.1mt for Group 700 (Weapons).

Plugging this into my Pre-Processor Spreadsheet (which I have modified a little over what is posted on my website) I get an estimate of about 3,429mt full load displacement.

At this point a question has come up that I'm not sure how to address. In general, I had set up my Pre-Processor to help make initial estimates of a ship's size, and the Main Processor as a means of doing a more detailed set of calcs. In the more detailed calcs the user will typically include a Margin to help account for uncertainties and other small stuff that may get over looked. Ultimately this Margin gets applied to all the components of a ship's Light Ship weight (including the estimated weight of the Weapons and Sensors). As such, the question arises as to whether I should include this margin to the Weapon and Sensor Weights in the Pre-Processor as well to help ensure that the initial weights estimated here correctly match up with the weights ultimately estimated in the Main Processor.

If I were to do so, then the the total Weapon and Sensor Weight plus margins would be about 246.2mt, which would suggest a total displacement of about 3,653mt.

Plugging this into the equations in the next step in my Pre-Processor, suggests a Length of about 113.0m, however looking at the actual plot suggests that my curve fit may not be that good, and I should probably try and re-analyze the data to see if I can get a better fit. Looking at this plot suggests a Legth of about 120m or so would be a better estimate, which is close to the actual length of the ship of 124.4m.

Plugging this into the next step of the spreadsheet gives an estimated Beam of 14.36m which is close to the maximum Beam listed for the ship of 14.3m but a bit above the waterline(?) Beams listed of 13.7m.

Similarly, the spreadsheet equations gives a suggested Depth of about 9.90m, though there is a fair amount of scatter in the data. 9.90m is a bit higher than the listed Depth of the ship of about 9.14m but 9.14m is well within the scatter of the data.

Going to the next step gives an estimated Installed Power very close to the actual installed power of 40,000HP though the installed Generating Power seems a bit low at 2044kW.

Similarly, the estimated Accomodations size is about 174, which isn't too far off the listed 176-179 I found in the sources listed previously, but less than the 193 persons listed for the ship later in its life.

I'll try and post the reults of the next set of calculations (from the Main-Processor) later.

If you have time, you could offer up a spread of "proposals" by displacements and beams by way of a "faux timeline". The lighter weight could be "early" in the design, and the heavier weights near the end, with a "compromise" via using a middle weight proposal to permit greater growth over time.

In my case, I've gone for months (years) with one length, only to find now that I had to fix my 1/2 entrance angle to avoid costly fuel burn. Visually, my model looks close various hulls of ships of its size, but programmatically, with an 84 degree ie and 7.4 m draft, I had to go down to 7.3 m for about 60 deg and 7.2 m about 21 deg. But, fiddling with the bow got me to about 1.5 deg -- too find and might contribute to plunging or too much wetness (although I've got a very, very wide focsle, high up enough that wetness should not be a problem at most speeds, but, still, too much flare is lots of mass, and that mass is loss of buoyancy in some sea states).

As for depth, my weather deck is at about 11 m, and the keel at about 2.8, so, I'm at about 9-9.2m depth. Beam is ~19 m, give or take, depending on the draft. My fun this weekend involved crawling all over my curves refairing them to cut resistance and aid in decreasing the 1/2 entry angle. After a few hours, I got it down from ~84 to ~61, and that brough the resistance down from about 160,000 kN to about 48,000 kN. The length changed from 171 m wl to about 168.9 m wl due to changing the rake. But, i shortened my sonar dome from the experimental, longish one to one that is still farther protruding than the Kongo/Atago/Burke/Sejong. Every time I do that, I need to rerun my propulsion, acceleration, turning, SSD curves, and engine powering reports. Time files -- even though little gets done.

All that got going because I scaled a type 23 hull to closer to my own hull and found some attractive improvements in the hydros. That type 23 seems comparable to one of the DDG-51 3D hull hydros models.

Actually, belay my hydros values in my prior post. I mixed up the units/values. Here are some comparisons of one hull with a minor <1-meter length adjustment at the bow rake, and the difference between cleaning up lines and shortening the sonar dome length. I did not make an intermediate save with values of JUST the sonar dome change effect. I could now, but it would be very tedious since there were numerous downstream flow changes that might distort the presentation anyway, unless the hull were already well optimized but then fitted with a 2 m longer sonar.

I modeled my hull in Delftship, took it to Free!ship, then did some back and forth and then a movement of it back into Free!ship. The cacls I'm including below do NOT included the effects of wind, sea states, or unstable operation/attitude of the ship. I have the superstructure, uptakes, radar mast, guns, helo hangar, and such on the model, and included in the weights and other hydros. I'll later on run and show the aero effects and the cross curves & SSD calcs. Each takes abuut 2 to 30 seconds, depending on whether I run real vs bogus values and whether -- in the case of SSD and cross curves -- I set a large draft range (6000 t to 13280 t) with small displacement increments, such as 100 tons vs 500 tons (~ 50 seconds and ~20-30 secs, respectively).

Program of resistance and power prediction for naval ships (NUoS,Ukraine,2010).

Yeh, the thing about free!ship is that it counts draft starting from sonar/bulb base/bottom. But, it looks at the hull model surface and works with that, too. I'd visually prefer the dome be descriptively considered an appendage/extrusion/protrusion rather than the beginning of baseline. It'd be nice if FS/DS did that, and then allowed the user to seal off the knife edge, but automatically "seal" the supplied or in-app adjusted domes/bulbs so the user can model a desired dome shape compatible with the hydros and the flowlines that generally (simplistically) approximate CFD flow lines. It would remove a lot a the tedium and enable the user to create an array of possible domes/bulbs a lot faster.

I may be incorrectly interpreting things, but if the hull Pe required is less than the installed power, then it seems to me that physically, the hull should reach that speed given the excess power. This is assuming the sea state permits it, there is no surge eroding the advance, the winds are fair, and the plant condition optimal or very high. If the props and hull are not negatively/adversely fouled, and the Pe is less than the the installed power, and if the Pe is 60,000 kN, and the engines and BHP and SHP and EHP are contributing to an excess, I am inclined to think the hull will reach those speeds I set as maximal speed. I could be mistaken, though. (Of course, various appropriate/applicable methods would be needed for validation of the predictions. I mainly look at Holtrop and at Fung-Leibman although I look at one or two others for sea ships just to compare. Nicely, though, free!ship will warn the user that the method is not appropriate for the model, and the model coefficients are used to determine if the model should be a proper subject of a method.

It seems to me that the designers/marketers of a hull who manipulate a prospective buyer's expectations either are willfully doing so, or they are using tools that do not professionally or ethically warn them that the chose prediction method is not appropriate (morally/ethically/professionally/hydrodynamically/etc.) I like the V. Timonshenko added those appropriateness checks to the program. That is really cool of him. The program in text output in the report and programmatically in the GUI by way of blatant warning and prolonged calc time warn the user that one or more input variables is missing or incorrect or not appropriate.

It might be helpful if you could post an image of your midships section or provide an estimate of how far below the keel your bulb extends. Right now, since the Midships and Block Coefficients appear to be based on the draft to the bottom of the bulb it may be that they are affecting your resistance calcs (I notice an error message suggesting that the"Cm" used appears to be outside the range for the Fung method).

With regards to my FFG-7 estimates, here is a summary of the Main-Processor calcs.

In general, many of the recommended values and outputs from this module are close to the published values for the ship including the overall total displacement, though in the actual individual weight categories have some variations (especially Structural weights and Auxiliary weights for example). Part of this might be due to the actual FFG-7 having an Aluminum Superstructure, whereas the trendline that the calcs are based on included both ships with Aluminum and Steel Superstructures. However, it should also be noted that there is sometimes variations in the range of all the individual weight groups in different published sources as well.

Hopefully, tomorrow or the next day I will try and post some additional information to show how the individual calcs in this model compared to the known data.

It is from May 2011, and is mercifully only 7 pages long, but is interesting nevertheless. It might influence your decision of using the FFG-7 model with its one shaftline to considering and using 1 GT on two shaftlines, with more fuel efficient diesels for cruise powering two 2+MW motors. In any case, there are some surge, sway, and yaw formulas you likely already know or use.

(Readability would be easier if internationally we all agreed to put an unused line between paragraphs and to not rely on forced-short sentences to provide white space. I realize technical papers writers have space or length constraints, and lines mean ink, but... an argument for a different topic...)

The model simulates an LM2500, used in Italian-French FREMM and German F125. Seems to make a good case for using cross-connected gearboxes in frigate-sized combatants, regardless of which navy/nation builds the ship, to me. Redundancy, flexibility, power modes, reduced hull-borne noises, reduced vibrations, and fuel-savings are attractive.

I here is the output from my hullform calcs. This 1st image shows both a profile and deck plan view of the FFG-7 that I located on the internet

Additionally, here is a simple Body Plan that I also located in a document on the internet.

Using this information, I then approximated the Profile of the ship in the Hull Post-Processor spreadsheet, as shown below.

I next took the output data from the Main-Processor and drew up the Prismatic Coefficient curve for the ship, as shown below. Here I have plotted the the estimated curve for the ship over a set of curves that I have for several 1970-1980 era Frigates (that I believe came from an ASNE Journal article by Kehoe & Brower that I will try and locate later).

Unfortunately, as can be seen it is not an exact match but is similar to the actual ship's curve. Next, I also plotted up the ship's Design Waterline and tweaked some of the terms to develop a suitable curve. This is also plotted against data for a set of typical Frigates as well.

(It should also be noted that there appears as if there is a possible flaw in my original scans as the X-Scales on both sets of original sets of data doesn't seem to fully scale correctly.)

Next, I approximated an Intermediate Deck as shown below (but I do not currently have anything to compare that against yet.

Taking all this data together, I then was able to develop up a Body Plan for the ship. Once again, as can be seen it is not an exact match for the actual ship's body plan but it does appear to be a reasonable approximation for the ship. I may tray and better estimate the Intermediate Deck shape for the ship and try and redo the Body Plan later.

Finally, here is a rough check of the Hull's Seakeeping and an estimate of the hull's total volume.

As can be seen above the ship is estimated to have fair seakeeping form this calc. The total estimated enclosed volume of the hull is 10,887 cubic meters, as compared to the actual value listed above of 10,721 cubic meters (378,590 cubic ft)

These pages should interest you (those with asterisks ** particulary show FFG-7, among other vessels, and should help you super-tweek/tweak your spreadsheets):

2. "B-2.1 Curves of Form. Curves showing hydrostatic characteristics of a ship’s hull are prepared by the designers. These curves are normally
presented in a single document called the Curves of Form, Displacement and Other (D & O) Curves, or Hydrostatics Curves. This set of curves
is often the single most useful document to a salvage engineer. Curves of Form are carried aboard Navy ships, usually in the custody of the
Engineer or Damage Control Assistant. Figure FO-2 is an exact copy of the Curves of Form prepared by the designers for the frigate FFG-7
and other ships of the same class. On newer ships, the Curves of Form are presented on a single drawing with the Cross Curves of Stability
and the Bonjean’s Curves. The following information is available from the Curves of Form for Navy ships:"

5 & 6: Flooding Diagrams, calcs and how used

13. ESWBS & SWBS

16. "B-4.4 Obtaining and Using Ship’s Drawings. Navy ships carry an abridged drawing set, called the selected record drawings, consisting of the
drawings used most often by ships force. On newer ships, the bulk of the selected record drawings are provided on aperture cards (microfilm).
Before depending on use of a ship’s selected record drawings the salvage engineer should ensure that he has access to a working aperture card readerprinter.
Lens for ordinary microfiche readers can not view an entire aperture card film." [[[probably requires a specially-magiced decoder ring to activate the special lens...]]]

18. B-4.4.1 Numbering System for Older Drawings

18..... "B-4.4.2 Type Designator/Hull Number Changes. Type designator and hull number are sometimes changed during the ship’s life or planning, so the designator/hull number for a drawing may not correspond the ship type and number. For example, many FFG-7 class drawings are cataloged as PF-109 drawings because that was the designator originally assigned. Similarly, drawings for most FF- 1052 class ships are cataloged as DE-10XX."

For all others, whether designng real, never-were, or fantasy/notional/plausible combatants, or designing merchant ships, the entire document is an instructive treasure trove and an example of brevity/concision.

((((Now, if only the document (or any product brochures i CAN find gave any clues as to the typical ranges/bands of engine power and inertia moments by engine for Gas Turbines Engines... ie, does an LM2500/WR21/MT30 operate in 60-80 kg m^2 or 200-600, or 800-2000? Does the engine power NEED to be as high as 110000kw, or can it be as low as 40,000kw? If 4 engines produce 75,000 kw to 110300kw, then will a max of 30mw be sufficient for the props motors or reduction gear output to the shafts? I can mix all sorts of combinations to reach 3D model/predicted speeds of 42kts +, using 4 different prediction methods by WELL respected persons, but the outputs don't satisfy me unless I know I'm inputting valid power bands.))))

"DDG 51 hull has transom stem. During the model experiment we observed that at ship
speed greater than 20 knots the flow clears the stem completely and the cross section becomes dry.
In order to model this physical phenomena numerically, we impose two conditions at the stem.
First, to satisfy the dry condition at the cross section of the transom stem, we do not put any
panels to represent the cross section and leave it empty, in other words, the ship hull is not closed
at the stem. Secondly, at the bottom edge of the transom stem, the body boundary condition of
Eq.(7) is replaced by the requirement that the flow pass by each bottom edge panel tangentially.
The magnitude of the tangential velocity is assumed equal to square root of the hydrostatic term
2gh of Bernoulli equation...."

If your Pre-Process or Main Processor, or Post Processor spreadsheets (hehehe, I'm thinking of Mr. Peabody and his 3D-BB (3-Dimensional Blackboard) and Sherman for some reason when I see those terms) someday support damaged stability, free-communication flooding, and sec mod estimates, that would probably amaze and startle different sets of people. Imagine a spreadsheet doing what some $10,000/seat GUI programs are doing, hehehehe....